Roots, xylem and phloem

Organisation · Plant tissues, organs and systems · note 3 of 5

Spec 4.2.3.2Download all Plant tissues, organs and systems notes (PDF)Download all notes (PDF)6 pages

Roots, xylem and phloemSpec 4.2.3.2

In short

The roots, stem and leaves form a plant organ system for transport. Root hair cells absorb water by osmosis and mineral ions by active transport, helped by a large surface area and many mitochondria. Xylem, made of hollow tubes strengthened by lignin, carries water and mineral ions up the plant. Phloem moves dissolved sugars by translocation.

The roots, stem and leaves form a plant organ system for transport of substances around the plant.

Root hair cells

Root hair cells are adapted for the efficient uptake of water by osmosis and mineral ions by active transport.

The long root hair gives a large surface area for taking in water and mineral ions.
Mineral ions are usually at a lower concentration in the soil than in the cell, so they move into the cell against the concentration gradient by active transport. This needs energy from respiration, so root hair cells contain many mitochondria.
Water moves in by osmosis.

Xylem

Xylem tissue transports water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin. It is adapted for the transport of water in the transpiration stream.

Phloem

Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. The movement of food molecules through phloem tissue is called translocation.

Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls.

Xylem and phloem compared
	Xylem	Phloem
Transports	Water and mineral ions	Dissolved sugars
Direction	From the roots to the stems and leaves	From the leaves to the rest of the plant
Structure	Hollow tubes strengthened by lignin	Tubes of elongated cells with pores in the end walls
Process	Transpiration stream	Translocation

Exam tip:

The detailed structure of phloem tissue and the mechanism of transport are not required, so just learn what is written above.

A root hair cell with a long root hair among soil particles, with mitochondria and a nucleus, showing water entering by osmosis and mineral ions entering by active transport. — Water enters by **osmosis**. Mineral ions enter by active transport, using energy from the mitochondria.

Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026

Frequently asked questions

How does water move from roots to leaves?

Water enters root hair cells by osmosis, then moves up through the xylem to the leaves in a continuous flow called the transpiration stream. In the leaf, water evaporates from the surface of the mesophyll cells into the air spaces, and water vapour diffuses out through the stomata. This loss of water vapour from the leaves is transpiration.

How does light intensity affect the rate of transpiration?

Increasing light intensity increases the rate of transpiration, because stomata open wider in the light, so more water vapour can diffuse out of the leaf. In darkness the rate falls. Higher temperature and more air movement also increase the rate of transpiration, while higher humidity decreases it. A potometer can be used to measure these effects.

What is the difference between xylem and phloem?

Xylem transports water and mineral ions from the roots to the stems and leaves in the transpiration stream, and is made of hollow tubes strengthened by lignin. Phloem transports dissolved sugars from the leaves to the rest of the plant by translocation, and is made of tubes of elongated cells with pores in the end walls.

All 4 questions on Plant tissues, organs and systems